Work on the project will be continued along the following lines: 1. Study of rotational diffusion of small molecules (mol. wt. less than 500) by differential phase fluorometry, to characterize the motions in media with hydrogen bonding properties and without them. Preliminary observations have shown very large differences in these cases. The importance for the interpretation of data from fluorescence probes included in membranes is obvious. 2. Development of the variable frequency cross-correlation fluorometer is continuing and we expect substantial progress in the next three months. 3. Study of ligand binding to proteins, and of fast spectral relaxation of fluorescence of bound fluorophores. This is alos being followed by differential phase fluorometry using optical filters that permit separation of the unrelaxed (blue) and relaxed (red) components. 4. Studies of the fluorescence of proteins and protein-ligand complexes at high pressure (1-10 Kbar). The equilibrium of the flavin-binding protein of hen's eggs with flavin mononucleotide is being studied and a very clear characterization of a loss in binding properties with a characteristic pressure of 4.5 Kbar is being followed. Preliminary technical developments to measure fluorescence polarization at high pressures will be carried out.